How to use the ipysheet.to_dataframe function in ipysheet

df = ipysheet.to_dataframe(sheet)
    assert np.all(df['t0'].tolist() == [2,   1,   2,   2])
    assert np.all(df['t1'].tolist() == [34,  1,   2,   0])
    assert np.all(df['t2'].tolist() == [543, 1, 222, 111])
    assert np.all(df['t3'].tolist() == [23,  1,  22,  11])

    sheet = ipysheet.sheet(rows=0, columns=0)

    df = ipysheet.to_dataframe(sheet)
    assert np.all(df == pd.DataFrame())

    sheet = ipysheet.sheet(rows=4, columns=1)
    ipysheet.column(0, ['2019/02/28', '2019/02/27', '2019/02/26', '2019/02/25'], type='date')

    df = ipysheet.to_dataframe(sheet)
    assert [_format_date(x) for x in df['A'].tolist()] == ['2019/02/28', '2019/02/27', '2019/02/26', '2019/02/25']

def test_to_dataframe():
    sheet = ipysheet.sheet(rows=5, columns=4)
    ipysheet.cell(0, 0, value=True)
    ipysheet.row(1, value=[2, 34, 543, 23])
    ipysheet.column(3, value=[1.2, 1.3, 1.4, 1.5, 1.6])

    df = ipysheet.to_dataframe(sheet)
    assert np.all(df['A'].tolist() == [True,   2, None, None, None])
    assert np.all(df['B'].tolist() == [None,  34, None, None, None])
    assert np.all(df['C'].tolist() == [None, 543, None, None, None])
    assert np.all(df['D'].tolist() == [1.2,  1.3,  1.4,  1.5,  1.6])

    sheet = ipysheet.sheet(rows=4, columns=4, column_headers=['c0', 'c1', 'c2', 'c3'], row_headers=['r0', 'r1', 'r2', 'r3'])
    ipysheet.cell_range(
        [
            [2, 34, 543, 23],
            [1,  1,   1,  1],
            [2,  2, 222, 22],
            [2,  0, 111, 11],
        ],
        row_start=0, column_start=0,
        transpose=True
    )